Interferon gamma produced by mitogen-activated T lymphocytes does not directly mediate lymphoproliferation

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Abstract
Human interferon gamma (IFN‐γ) endogenously produced during mitogenic stimulation of human peripheral blood mononuclear cells or human T lymphocyte‐enriched cultures was neutralized in situ by the addition of a polyclonal antiserum (anti‐L) raised in a rabbit against partially purified natural IFN‐γ derived from peripheral blood mononuclear cells. Small decreases in mitogen‐induced [3H]thymidine incorporation (lymphoproliferation) were demonstrated under these conditions. However, an antiserum (anti‐G) raised in a sheep against highly purified recombinant IFN‐γ (E. coli‐derived) which strongly neutralized the antiviral effect of IFN‐γ either had little effect on mitogen‐induced lymphoproliferation or caused slight enhancement of mitogenesis. The interleukin 2 responsiveness of activated T lymphocytes following mitogenic stimulation was not found to be different in the presence of anti‐G to that of control cultures incubated in the presence of normal sheep serum. These results suggest that IFN‐γ is not a direct requirement for lymphoproliferation.